Te Waha Nui report by Skye Wishart
Hikers in the Waitakeres can expect track closures in July to limit the spread of kauri dieback disease.
The closure of 27km of the Waitakeres’ 260km of tracks is to be approved imminently, says principal biosecurity advisor for the Auckland Council, Nick Waipara.
The goal is to create disease-free sanctuaries and cut off areas infected by the kauri-killing water mould Phytophthera taxon Agathis, or PTA.
The disease, commonly called kauri dieback, is thought to be spread by soil movement.
The decision comes after surveys showed that the 100 or so boot-washing stations put in place were largely ignored by the public who did, however, respect track closures when they were trialled in spring over the past two years.
“We had a much higher compliance with track closures than with cleaning stations,” said Waipara.
Helicopter and ground surveys suggest that 13 per cent of the kauri in the Waitakeres is visibly infected with PTA. Almost 70 per cent of these diseased trees are located near tracks.
Infected trees develop yellowed leaves, dying branches and a thick, sticky “pus” oozing from rotting bark. Moving up from the base of the tree, the rot can advance at 9cm per year.
PTA spores can sit dormant in the soil for years. When it rains, they release little mobile “zoospores” that can move around in the soil and invade susceptible roots.
Time until the trees’ death varies, but in the lab, young potted kauri can die three weeks after infection.
Waipara says despite the track closures, there are still many options for hiking — on alternative tracks.
“You can still get to the Tom Thumb tree [for example] by other tracks.
“Closing one track in southern Huia didn’t work, because fishermen use it, and they weren’t going to bush-bash.
“We know there are limitations [to which tracks we can close]…when there are no alternatives.”
The president of the Auckland Tramping Club, Graeme McGowan, says most trampers are very environmentally aware and will support further closures if they are kept informed on their effectiveness.
“If there’s evidence that [the disease] is spread through people’s movement then the vast majority would respect it,” he said.
“But we need the [dieback management] team to say ‘Yes, it’s really making a difference’. We need communication.
“Close the tracks, but once every 12 months, or whenever, come back and tell us what’s happening.
“I hope that it will be combined with a good public awareness campaign because tramping clubs only make up part of the total number of people [using the tracks].”
Waipara says pigs are another risk in the spread of PTA, and the council has trebled pig-culling contracts in the Waitakeres since 2009.
“[Pigs] move a lot of soil just through their feeding behaviour.”
Pigs may also spread the disease if they eat infected roots and move to another area.
Plant pathologist Stanley Bellgard, of Landcare Research, says the sooner more areas are closed off, the better.
“As we accumulate evidence, we’re losing trees. We don’t have the luxury of gradualism.”
He is working on the problem with other scientists from Landcare Research, Scion and Plant & Food Research.
Today, kauri dieback is found in the Waitakeres, Omahuta plantations, Glenbervie, Russell Forest, Okura, Albany, Pakiri, Trounson Kauri Park and Waipoua Forest.
The Kauri Dieback Management Team is a joint agency response team made up of DOC, MAF, the four regional councils of Northland, Auckland, Waikato and the Bay of Plenty, and the maori group Tangata Whenua Roopu. The team contracts the scientific research institutes.